Hi Wil, and welcome to the club.
I am guessing that your car has the 2.7Diesel V6, which is the same engine at the Diesel S Type which I have.
If this is so, your car will have a cam belt which should be changed after either 105,000 miles, or 10 years.
Regards,
Peter.
PS. I have just seen a list of fixed prices from Lancaster Jaguar Tamworth which list the cam belt change price at £375 for your model.